Various types of performance aspects including, for example, driveability, exhaust emissions performance, and a fuel consumption rate, are required of an internal combustion engine for automobiles. Receiving requirements concerned with these aspects of performance issued from a controller for controlling an entire vehicle, a control apparatus for the internal combustion engine controls control amounts for the internal combustion engine so as to satisfy these requirements. In reality, however, it is difficult to achieve completely all of these requirements simultaneously. Thus, a technique needs to be devised for properly incorporating the requirements of various types in the control amounts for the internal combustion engine.
JP-A-2009-162199 discloses an example of such a technique. A control apparatus for an internal combustion engine as disclosed in this publication incorporates various types of requirements in control amounts for the internal combustion engine by performing mediation of requirements. In the mediation of requirements, each of the requirements is first expressed by a predetermined physical quantity. The physical quantities herein used are to be used as the control amounts for the internal combustion engine, including, for example, torque, efficiency, and an air-fuel ratio. Efficiency refers to a ratio of torque actually outputted to torque to be potentially outputted by the internal combustion engine. Next, values of requirements expressed by the same physical quantity are collected. A predetermined calculation rule is then applied to determine a single value from the plurality of requirement values. This process of determination is called the mediation.
The “mediation of requirements” is based on an assumption that all requirements to be mediated are expressed by the same physical quantity, or more precisely, a physical quantity used as a control amount. Accordingly, each of all requirements outputted from the vehicle controller to the control apparatus for the internal combustion engine should be expressed in a form of a requirement value of the control amount. It is, however, conceivable that taking the form a particular control amount is not necessarily appropriate depending on the type or details of the requirement. In such cases, the requirement may not be appropriately incorporated in the target value of the control amount.
Among the requirements concerned with performance of the internal combustion engine, some may be appropriately expressed by a time-integrated value, instead of an instantaneous value, of the control amount. A good example of such requirements is a requirement concerned with exhaust emissions performance during cold starting. The exhaust emissions performance during cold starting depends on an activated state of a catalyst. An exhaust emissions temperature or efficiency relating thereto may therefore be used as the control amount to incorporate the requirement. Note, however, that it is the time-integrated value of the exhaust emissions temperature that affects the activated state of the catalyst and the exhaust emissions temperature varying from one time to another does not change greatly the activated state of the catalyst. Consequently, where feasible, the time-integrated value of the exhaust emissions temperature is preferably used as the requirement value of the control amount in terms of the exhaust emissions performance during cold starting.
However, in actual control procedures, it is the instantaneous value of the control amount that the control apparatus can mediate. Even if the time-integrated value of the control amount is outputted as a requirement, the control apparatus is unable to mediate the requirement with others. When the “mediation of requirements” is performed, therefore, a requirement can be outputted only in the form of the instantaneous value of the control amount, even if the requirement is appropriately to be represented by a time-integrated value. This results in the following. Specifically, in mediation based on a comparison made in terms of instantaneous values, a requirement is placed in a lower priority than the others even though the requirement should be given priority, so that the requirement is not incorporated at all in a final mediated value, specifically, the target value of the control amount. In contrast, a requirement having a relatively low priority is given too high a priority as a result of mediation based on a comparison made in terms of instantaneous values. This may hamper other requirements to be given priority from being incorporated in the target value of the control amount.
To control the internal combustion engine appropriately, it is necessary to incorporate also requirements concerned with the time-integrated value of the control amount appropriately in the target value of the control amount, in addition to requirements concerned with the instantaneous value of the control amount.